Percutaneous transluminal coronary angioplasty (PTCA) is used to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. Typically a guidewire is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the guidewire and a balloon catheter advanced within the guiding catheter over the guidewire. The balloon at the distal end of the catheter is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten re-closure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel collapse. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in size from 3.0 mm in the coronary vessels to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. Stents radially expand as the balloon is inflated, forcing the stent into contact with the body lumen thereby forming a supporting relationship with the vessel walls. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter.
Various shapes of stents are known in the art. U.S. Pat. No. 4,649,922 to Wiktor for "Catheter Arrangement Having A Variable Diameter Tip and Spring Prothesis" discloses a linearly expandable spring-like stent. U.S. Pat. No. 4,886,062 to Wiktor for "Intravascular Radially Expandable Stent and Method of Implant" discloses a two-dimensional zig-zag form, typically a sinusoidal form. U.S. Pat. No. 4,969,458 to Wiktor for "Intracoronary Stent and Method of Simultaneous Angioplasty and Stent Implant" discloses a stent wire coiled into a limited number of turns wound in one direction then reversed and wound in the opposite direction with the same number of turns, then reversed again and so on until a desired length is obtained. U.S. Pat. No. 5,133,732 to Wiktor for "Intravascular Stent" discloses a stent body coiled from a generally continuous wire with a deformable zig-zag structure with a means for preventing the stent body from stretching along its longitudinal axis.
U.S. Pat. No. 5,019,090 to Pinchuk for "Radially Expandable Endoprosthesis and the Like" discloses a plurality of adjacent generally circumferential sections that are substantially axially positioned with respect to each other. At least one of the generally circumferential sections has a generally circumferentially disposed expandable segment that imparts circumferential and radial expandability to the stent.
U.S. Pat. No. 5,104,404 to Wolff for "Articulated Stent" discloses a stent made up of a number of wires welded together and then connected together with hinges to provide articulation.
U.S. Pat. No. 5,116,365 to Hilistead for a "Stent Apparatus and Method for Making" discloses a stent constructed from two elongated wires which are each bent into a series of tight bends. The two wires are permanently adhered at a first interconnection junction. The two wires are then wrapped around a mandrel repeatedly forming two opposing series of interconnections.
U.S. Pat. No. 5,161,547 to Tower for a "Method of Forming an Intravascular Radially Expandable Stent" discloses a stent formed from a fine wire bent into a serpentine flat ribbon which is wound around a mandrel into a cylindrical sleeve and welded to a pigtail of the wire.
U.S. Pat. No. 5,342,348 to Kaplan for a "Method and Device for Treating and Enlarging Body Lumens" discloses a delivery matrices which provide for the controlled release of bioactive substances. The tubular structure includes a perforated cylinder and a filament is interwoven through the perforations in the cylinder.
U.S. Pat. No. 5,354,308 to Simon for a "Metal Wire Stent" discloses a frame adapted to assume a first condition in which the frame is relatively rigid and substantially tubular in configuration and a second condition in which the frame is flexible, of reduced stress, and collapsible, such that the second condition walls of the frame are adapted to be positioned against each other to form a stent diameter substantially equal to the combined thickness of the frame walls in abutting engagement with each other, the frame in its second condition being substantially devoid of bias therein urging the frame to assume the first configuration. The tubular body mesh may be formed of polygonal or hexagonal cells.
U.S. Pat. No. 5,443,498 to Fontaine for "Vascular Stent and Method of Making and Implanting a Vascular Stent" discloses a continuous wire which is formed into a substantially tubular body having a plurality of oblong, open cells which are staggered around the circumference of the tube. When the body is formed in its unexpanded state, the long sides of each oblong cell are arranged substantially parallel to the longitudinal axis of the tubular body. Adjoining cells may then be bonded together at a point between adjacent parallel sides on a cell. When the body is expanded, the adjacent sides of each cell extend oblique to the longitudinal axis of the body.
Co-pending patent U.S. Ser. No. 08/426,310 to Boyle et al. for "Bidirectional Dual Sinusoidal Helix Stent" discloses a first sinusoidal wave form wrapped around a mandrel such that the sinusoidal helix wraps form an acute angle with respect to the forming mandrel. The second sinusoidal wave form is wrapped around a mandrel such that the sinusoidal helix wraps form an obtuse angle with respect to the forming mandrel. The two sinusoidal helix wave forms are connected only at the two ends of the stent. The waveforms are not interconnected along the length of the stent.
WO 94/12136 to Anderson et al. for "Stent for Body Lumen Exhibiting Peristaltic" discloses knitting preferably a nitinol wire into a pattern of overlapping loops selected such that from a relaxed state each row of loops may shift axially relative to and independently of the rows on either side.